1. Field of the Invention
This invention relates to inflation packers used in downhole casing, and more particularly, to a casing inflation packer with a rupture disc for opening in response to a predetermined pressure and allowing inflation of the packer, a pressure actuated valve for closing in response to a second predetermined pressure so that the packer is not overinflated, and a metal bladder within the packer element for support thereof.
2. Description Of The Prior Art
In preparing oil well bore holes for oil and/or gas production, an important step involves the process of cementing. Basically, oil well cementing is the process of mixing a cement-water slurry and pumping it down through steel casing to critical points located in the annulus around the casing, in the open hole below, or in fractured formations.
Cementing a well protects possible production zones behind the casing against salt water flow and protects the casing against corrosion from subsurface mineral waters and electrolysis from outside. Cementing also eliminates the danger of fresh drinking water and recreational water supply strata being contaminated by oil or salt water flow through the bore hole from formations containing these substances. It further prevents oil well blowouts and fires caused by high pressure gas zones behind the casing and prevents collapse of the casing from high external pressures which can build up underground.
A cementing operation for protection against the above-described downhole condition is called primary cementing, and the present invention is generally useful in such cementing.
One prior art type of casing inflation packer utilizes a knock-off pin and initial control valve. The initial control valve contains relatively small O-rings requiring difficult manufacturing techniques. Also, these O-rings may be inadvertently cut when the packer is installed and possibly during downhole operations.
The knock-off pin of the prior art packer protrudes into the inside diameter of the valve body. The knock-off pin is sheared by pumping a plug downwardly thereto or by manipulation of a work string in the casing. In some cases, the knock-off pin has prevented the plug being pumped from seating properly.
The present invention solves these problems by using a rupture disc which prevents the packer from being inflated until a first predetermined pressure is attained inside the casing. A shearably attached initial control valve is disposed between the rupture disc and the inflatable packer and is designed to close in response to a second predetermined pressure so that the packer is not overinflated. Once closed, the control valve locks in the closed position, thereby preventing the packer from deflating. A secondary back pressure valve with an elastomeric lip acting as a check valve keeps the packer inflated should the control valve fail. The same type of check valve is used at the other end of the packer to keep pressure equalized inside the packer as the tool is being placed downhole.